Engine controllers control many engine operational parameters such as air charge, fuel charge, exhaust gas recirculation, fuel vapor recovery, ignition timing, camshaft timing, valve timing, and so on. These parameters are controlled to achieve desired engine power while minimizing emissions.
Control of these parameters requires knowledge of camshaft position. Typically, a toothed wheel with one or more missing teeth is positioned on the camshaft and a detection of the passing teeth determines camshaft position.
Engine controls are more complicated in vehicles equipped with variable cam timing. Camshafts are driven by belt or chain couplings to the crankshaft. For engines equipped with variable cam timing, the timing or phase of the camshaft varies relative to the crankshaft. An electric motor or hydraulic actuator turns the cam relative to the crankshaft.
The inventor herein has recognized various issues with the above approaches. When the engine is being cranked during an engine start, detection of the passing cam teeth, or other detection method, may not provide accurate cam position measurement, which usually requires detection of several rising and falling edges. Often, a default cam position is used based on last known position or a designed rest position. In engines equipped with electrically controlled cam timing, the last cam position may not be known because the camshaft position relative to the crankshaft was disturbed by the torque applied to the camshaft after the engine was shut off and during startup before cam position is accurately measured. As a consequence, the engine controller may not accurately determine cam position during engine cranking. Without accurately knowing cam position, any estimate of air charge in the combustion chamber may be in error and consequently the air/fuel charge may be inaccurate, possibly resulting in longer engine starts and higher emissions. Similar issues may occur with other controlled operating parameters.
The inventors herein have solved the above issues with a method, comprising in one example the following: during cranking of an engine, driving a camshaft of the engine by an electric motor controlled by a motor controller which indicates motor position and position of the camshaft; determining one or more engine operating parameters for controlling the engine during the cranking by an engine controller from the indicated cam position; and after the cranking, identifying the cam position from a sensor coupled to the camshaft. By indicating cam position from the electric motor controller during cranking, the issues with the approaches described above during cranking are avoided. After engine cranking, when the engine has started, conventional mechanisms and methods for detecting camshaft position are used. Thus, the technical effect is achieved.
In one typical example, the motor comprises a brushless motor and the motor controller determines the motor position by decoding signals from three Hall Effect sensors coupled to a shaft of said motor. Further, the motor controller turns the motor to a desired position by feedback control based on the motor position determined from the decoded signals and the desired position.
In another example, the method comprises: during cranking of an engine, driving a camshaft of the engine by an electric motor controlled by a motor controller which indicates position of the motor and position of the camshaft; determining an amount of air inducted into a combustion chamber of the engine by an engine controller from the indicated camshaft position and speed of the engine; determining from the air amount a fuel charge to be delivered to the combustion chamber by the engine controller to start the engine during the cranking; and after the cranking, identifying the cam position from a sensor coupled to the camshaft, rather than from the motor controller, for use by the engine controller. In this way, accurate indications of camshaft positions are provided during engine cranking so that engine operating parameters such as air/fuel charge in the combustion chambers are accurately determined resulting in shorter engine starts and less emissions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.